Live viral vaccines are generally contraindicated in immunocompromised individuals at risk for replicating these viruses. However, measles itself has proven to be severe in children with HIV infection. Although vaccination of HIV infected children has been safe in studies to date, the immunogenicity of measles vaccine in this group may be suboptimal. Our laboratory is involved in an evaluation of antibody responses in a randomized, phase II study comparing one versus two doses of measles vaccin in infants (less than 6 months old) who were born to HIV-infected women. The 420 children will be randomized to either one of two measles immunization schedules: measles vaccine at 6 and 15 months of age or measles vaccine at 15 months of age. The children will then be followed fo 9 months after their vaccination. Of the 420 patients, 100 will be uninfected and 320 infected. For the 100 patients uninfected, 70 would be randomized to have 2 vaccinations and 30 to have 1 vaccination. For the 32 infected patients, one half would be randomized to have 2 vaccinations and the rest to have 1 vaccination. Our laboratory will be responsible for conducting Plaque neutralization tests (PNT) and ELISAs of sera from each subject at 0, 6, 22, 39, 45, 61, 78, and 130 weeks for Group A and 0, 39, 45, 61, 78, and 130 for Group B. ELISA reactivity will be compared to PNT titers. The study enrollment will begin in the fall of this year.